Modifier 90

New

I need some guidance on Modifier 90. I am coming from the Health Plan side of things, (Medi-Cal (CA) Managed Care, specifically), and I am looking for feedback on what type of providers typically use modifier 90 for their billing. I understand that the provider would use the modifier when they use a reference laboratory, and the lab would bill the provider, and the provider would bill the insurance. I need to know if every type of provider is using this modifier consistently, i.e. general practice, oncology, etc. Or if certain provider types use it more often than others. We are having issues with the restrictions that Medi-cal is placing on using this modifier, and are looking into making some adjustments to allow (hopefully), some ease of billing. Thank you for any and all information!!